1. Field of the Invention
The present invention relates to an electrical connecting structure and electrical connecting method for a piezoelectric element that deforms in response to a voltage applied thereto, a piezoelectric actuator that incorporates the piezoelectric element to drive an objective part according to deformation of the piezoelectric element, and a head suspension provided with the piezoelectric actuator. In particular, the present invention relates to an electrical connecting structure and electrical connecting method for a piezoelectric element, capable of conducting wiring work for the piezoelectric element in such a way as to prevent the piezoelectric element from being damaged and secure the reliability of the piezoelectric element, a piezoelectric actuator employing such a piezoelectric element, and a head suspension employing such a piezoelectric actuator.
2. Description of Related Art
Small-sized, precision information devices are rapidly advancing, and for use with such devices, needs for micro-actuators capable of conducting positioning control for very small distances are increasing. Such micro-actuators are highly needed by, for example, optical systems for correcting focuses and inclination angles, ink jet printers for controlling ink heads, and magnetic disk drives for controlling magnetic heads.
The magnetic disk drives are rapidly expanding market and improving performance, and accordingly, they are strongly required to increase their storage capacities. The storage capacity of a magnetic disk drive increases if the storage capacity of each magnetic disk contained in the magnetic disk drive is increased.
The storage capacity or recording density of a magnetic disk will increase, without changing the diameter thereof, if the number of tracks per inch (TPI) on the magnetic disk is increased. For this, the width of each track on the magnetic disk must be narrowed. To handle such narrow tracks on the magnetic disk, a magnetic head of a head suspension installed in the magnetic disk drive must conduct a precise positioning operation in a direction across the tracks, i.e., a sway direction. For realizing the precise positioning operation, an actuator capable of accurately moving and positioning the magnetic head in a very small area is needed.
To meet the need, the applicant of the present invention has proposed in Japanese Unexamined Patent Application Publication No. 2002-50140 a head suspension for a disk drive. The head suspension includes a base plate, a connection plate having a hinge thinner than the base plate, a load beam provided with a flexure and a slider, and a pair of piezoelectric elements.
This related art employs a dual actuator system that involves, for a precise positioning purpose, a voice coil motor and the piezoelectric elements made of, for example, PZT (lead zirconate titanate). The piezoelectric elements minutely drive a front end of the load beam or only the slider in a widthwise direction (sway direction) of the head suspension.
Compared with a single actuator system employing only a voice coil motor, the dual actuator system employing the voice coil motor and piezoelectric elements more precisely positions a magnetic head attached to a front end of the head suspension.
An important issue for the head suspension employing the dual actuator system is how to supply electricity to the piezoelectric elements.
A technique to approach this issue is disclosed in Japanese Unexamined Patent Application Publication No. 2003-61371 (in particular, FIGS. 9 and 10 thereof). This related art arranges a pair of wires on a head suspension. One of the wires is connected through wire bonding to a base electrode and the other wire is connected through wire bonding to an exposed part of the top face of each piezoelectric element.
This related art has a risk of cracking the piezoelectric element because the wire bonding process applies a local stress on the piezoelectric element to secure a bonding strength. If the wire bonding process is carried out with a reduced force not to crack the piezoelectric element, the bonding strength will be insufficient to deteriorate the reliability of electric connection to the piezoelectric element.
Instead of the wire bonding, a conductive adhesive such as conductive paste may be used to electrically connect each piezoelectric element to a wiring part such as a terminal part. The wire bonding or the conductive paste, however, causes a swell protruding from an end face of the piezoelectric element or an inclination of the terminal part, to make a clearance with respect to a magnetic disk insufficient.
In this way, it is very difficult to carry out wiring to the piezoelectric elements without damaging the piezoelectric elements or deteriorating the reliability thereof.